Aika is in love with a handsome teacher she admires, Tonami, while Mizuki tenderly cares for her younger sister. The sisters thought this sweet and bittersweet youth would continue, but… everything changed when Aika confessed to Tonami, saying she would do anything if he would date her! Instead of dating, Aika became obedient to Tonami’s whims, and one day, she found herself surrounded by Tonami’s so-called “friends,” strangers to her. Surrounded by these men, Aika, trembling with fear, was subjected to a hellish pleasure…

Mizuki, who shows a resolute demeanor as the student council president even towards the sexually harassing teacher, Tanabe. Despite feeling a sense of vulgarity from her beloved sister Aika’s uncharacteristic remarks, Mizuki sees her off to extracurricular service activities. However, when Mizuki is summoned by Tanabe, she is shown lewd footage of her sister, and in exchange for the promise to dispose of the video, she agrees to the man’s demands. As she experiences this for the first time, her consciousness begins to melt away, and she trembles with pleasure…!?

Under the promise that he would delete the porn video of her sister, Mizuki has been used and abused at Tanabe’s will for two days. Despite the pill they gave her, supposedly a contraceptive, making her act strangely, Mizuki continued to accept Tanabe. One day, while being taken outside, Mizuki encounters a scene where several female students from her school are having an orgy with numerous men. To her horror, among them is her beloved sister, Aika…